Cathode-ray tube with increased deflection sensitivity

ABSTRACT

A cathode-ray tube provided with an electron gun and a target electrode as well as a first image-forming lens, disposed in the path of the electron beam produced by the gun, for producing an intermediate image of the cross section of a selected point along the beam, which image is no greater than three times as large as the beam cross section, and a second image-forming lens disposed in the path of such beam downstream of the first lens in the direction in which such beam is traveling, for reproducing such intermediate image on the target electrode.

United States Patent Inventor Klaus Schafl'ernicht Ulm an der Danube, Germany Appl. No. 785,049 Filed Dec. 12, 1968 Patented Sept. 28, 1971 Priority Aug. 27, 1964 Germany T 26891 Continuation of application Ser. No. 482,533, Aug. 25, 1965, now abandoned.

CATIIODE-RAY TUBE WITH INCREASED DEFLECTION SENSITIVITY 17 Claims, 6 Drawing Figs.

US. Cl 315/17,

Int. Cl ..l'l0lj 29/46,

Field of Search 315/14, 17

[56] References Cited UNITED STATES PATENTS 2,383,751 8/1945 Spangenberg 315/14 2,954,499 9/1960 Gundert et a1.. 315/17 2,991,361 7/1961 Herrmann 315/17 X 3,225,248 12/1965 Scheffels 315/31 3,320,458 5/1967 Kobayashi 315/17 X Primary ExaminerMalcolm F. Hubler PATENTEU SEP28 1971 3,609,442

F ig l PRIOR ART Fig.5 F 5 n Klaus Saba #121322;

Attom CATI-IODE-RAY TUBE WITH INCREASED DEF LECTION SENSITIVITY C ROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 482,533, filed Aug. 25, 1965, now abandoned. The present invention relates to a cathode-ray tube, and particularly to a beam deflection system therefor.

In the usual cathode-ray tube, such as those used for oscilloscopes, for example, the crossover point of the beam, which is also known as the point of constriction of the beam and which is situated at some distance from the surface of the tube cathode, is reproduced on a fluorescent screen with the aid of an image-forming lens. Deflecting means for deflecting the tube electron beam in two mutually perpendicular directions are arranged between the lens and the screen. Additional electrodes may also be provided between the deflection means and the screen for effectuating a postdeflection acceleration of the electron beam. In the usual cathode-ray tube, the degree of deflection of the electron beams depends on the distance of the fluorescent screen from the deflection means and on the deflection angle. With a given maximum angle of deflection, the effective size of the fluorescent screen is determined by its distance from the deflection means. In practice, the larger the fluorescent screen, the greater must be the total structural length of the tube. The usual post acceleration actually serves to cancel some of the beam deflection, because the focusing action of an electrostatic postdeflection acceleration field causes the electron beam to be deflected to some extent back towards the axis of the tube.

It is a primary object of the present invention to permit a greater degree of electron beam deflection without increasing the power required by the deflecting means or the effective length of the tube.

It is another object of the present invention to increase the deflection sensitivity ofa cathode ray tube.

These results are achieved, according to the present invention, by providing, in a cathode-ray tube including an electron gun and a target electrode, an arrangement comprising: a first image-forming lens, disposed in the path of the electron beam produced by the gun, for producing an intermediate image of the cross section of a selected point along the beam, which image is no greater than three times as large as, and preferably the same size as, or smaller than, the beam cross section; and a second image-forming lens disposed in the path of the beam and downstream of said first lens, with respect to the direction of travel of the beam electrons, for reproducing said intermediate image on the target electrode.

Applicant has discovered that such an arrangement is highly advantageous because, taking into consideration all of the factors, such as structural length, necessary deflection power, aperture error, distortion errors, etc., involved in the design of a cathode ray tube, an optimum effect is obtained when the image of the cross section of the beam crossover point is produced, in the plane of the intermediate image, substantially on a 1:1 scale. Specifically, if this intermediate image has substantially the same size as the cross section of the beam crossover point, the tube can be dimensioned to have a minimum structural length for a given fluorescent screen size.

An improved cathode ray tube is also produced, according to the principles of the present invention, by constructing the image-forming lenses so that the second lens has a greater power of refraction than does the first lens.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIG. I is a diagrammatic side view of the beam deflection and focusing system of a cathode-ray tube according to the prior art.

FIG. 2 is a similar view illustrating a cathode-ray tube system representing a preferred embodiment of the present invention.

FIG. 3 is a diagrammatic side view of one type of imageforming lens which may be used in the device of FIG. 2.

FIG. 4 is a diagrammatic side view of another type of imageforming lens which may be used in the device of FIG. 2.

FIG. 5 is a diagrammatic side view showing a variation of the arrangement of one portion of the device of FIG. 2.

FIG. 6 is a view similar to that of FIG. 5 showing yet another variation of a portion of the device of FIG. 2.

In FIG. 1, there is shown a typical prior art cathode-ray beam deflection and focusing arrangement for directing an electron beam produced by an electron gun 1 onto a fluorescent screen 4. The beam produced by gun I has a crossover point, or point of constriction 2, at some distance away from the cathode of the gun. An image-forming or focusing lens 3, which is here represented symbolically by an optical lens, serves to focus the electron beam on the screen 4. The focal planes of the lens 3 are designated by the symbol f,. The lens 3 is followed by a deflection system comprising two deflection units 5 and 6 each of which acts to deflect the beam in a respective one of two mutually perpendicular directions over the plane of screen 4. From the figure, it can readily be seen that the degree of deflection of the electron beam over the screen depends on the distance of the screen from the deflection means and on the deflection angle, so that, with a given maximum angle of deflection, the size of the screen area traversed by the beam is proportional to the distance between the screen and the deflection means. Therefore, the only way to increase the screen size is to proportionally increase the total structural length of the tube. If the tube of FIG. 1 incorporated postdeflection acceleration of any prior art type, a reduction in the tube deflection sensitivity would result.

FIG. 2 shows a beam deflection system according to the present invention for overcoming the above-noted limitations on the effective screen size. An electron beam is produced by an electron gun 21 to have a crossover point 22 which is formed at some distance from the gun. A first image-forming lens 23 forms a real image 28, hereinafter referred to as the intermediate image" of the cross section of the beam crossover point 22 in a plane which is some distance away from the plane of fluorescent screen 24, the image 28 being at a relatively great distance upstream of the screen with respect to the direction of travel of the beam electrons. The lens 23 is so constructed that the size of the intermediate image 28 is no greater than three times as large as that of the cross section of the crossover point 22, the image 28 being preferably only as large as, or smaller than, the cross section of point 22. The above-noted 3 to l magnification has been found to be the maximum permissible because it constitutes the degree of magnification at which some deterioration in the quality of the image begins to be noted.

Although it is preferred that the intermediate image be that of the beam crossover point, the lens 23 can also be arranged to produce an intermediate image of a cross section of another point along the beam, such as that existing in the aperture of a diaphragm or that of a cathode spot.

A second image-forming lens 27 is disposed in the path of the electron beam between the plane of the intermediate image 28 and the fluorescent screen 24 for recreating the intermediate image 28 on the screen.

Horizontal and vertical beam deflection means 25 and 26, which are well known per se, are provided for controlling the sweep of the electron beam over the face of the screen.

The focal planes of the first image-forming lens 23 are designated by f, and those of the second image-forming lens 27 by f In case of using an accelerator lens as second imageforming lens 27 according to a preferred embodiment of the invention for example a lens as shown in FIG. 4, the screenside focal plane of the second image-forming lens 27 will lie nearer to the screen as it is designated by f in FIG. 2.

In the embodiment of FIG. 2, the deflection means 25 and 26 are disposed downstream of the first image-forming lens 23, with respect to the direction of travel of the beam electrons. However, the deflection means may also be arranged so that the lens 23 is disposed between them, as shown in FIG. 5, or so that they are upstream of the lens 23, as shown in FIG. 6. Each of the deflection means is shown to be in the form of a pair of electrostatic deflector plates, such as are commonly used in oscilloscope tubes. However, these deflection means could also be constituted by any well-known electromagnetic deflection coils.

The second image-forming lens 27 preferably has a greater power of refraction than the first image-forming lens 23. The refraction power of lens 27 determines the degree to which the electron beam will be deflected by this lens whenever the image 28 has been deflected away from the axis of lens 27 by deflecting means 25, 26. Thus, whenever image 28 is displaced from the axis of lens 27, this lens acts to substantially amplify the beam deflection angle as well as to reverse the direction of deflection imparted by the deflection means. Therefore, as may be seen from a comparison of the structures of FIGS. 1 and 2, the presence of the second image-forming lens 27 downstream of the deflecting means 25 and 26 acts to substantially increase the deflection sensitivity of the device without requiring any increase in the length of the'cathode ray tube structure or in the deflection power supplied to the deflection means.

It has been found to be particularly advantageous to construct lens 27 in the form of an electrostatic lens. Of course, a device constructed according to the present invention also performs well if one or both of the lenses are constituted by any suitable, well known magnetic focusing unit. it has been found, however, that the most favorable operation is obtained if the second image-forming lens 27 is constituted by an electrostatic accelerator lens such as that shown diagrammatically in FIG. 4. Such a lens consists, for example, of two successive cylindrical lengths of tube displaced from one another along the lens axis. The second tube encountered by the electron beam is connected to be at a higher positive potential than the first tube. Such a lens is highly desirable because it performs the two functions of recreating the intermediate image on the fluorescent screen and of effectuating the postdeflection acceleration of the electron beam. Whereas the post deflection acceleration arrangements in the prior art cathode-ray tubes invariably lead to a reduction in the overall deflection sensitivity thereof, the postdeflection acceleration effectuated by the second lens of the present invention has the opposite effeet, with the result that an increase in the postdeflection acceleration ratio in the device of the present invention leads to an increase in the power of refraction of the second lens and hence to an increase in the deflection sensitivity ofthe tube.

Both of the lenses 23 and 27 are preferably constructed in the form of axially symmetrical lenses. in certain situations, for example where it is desired to effect a further reduction in distortion errors, it may be desirable to provide the second image-forming lens with one or more additional auxiliary electrodes. Such a lens is shown diagrammatically in FIG. 3 in the form of an electrostatic lens unit having three electrodes with the center electrode being at either a positive or a negative potential with respect to the two outer electrodes. Generally, this lens unit will be of the axially symmetrical type having its two outer electrodes at the same potential. However, this unit may also be of the axially asymmetrical type wherein the two outer electrodes are at different potentials from one another. The first image-forming lens 23 is preferably constructed in the form of an axially symmetrical electrostatic lens unit, particularly when this lens is mounted upstream of the deflection means, because it is desirable to avoid as much as possible the creation of an excessively accelerated electron beam in the region of the deflection means.

The advantage of the increased deflection sensitivity of the present invention can be obtained even if the second lens is in the form of an axially symmetrical electrostatic lens unit. However, an additional postdeflection acceleration can only be applied to the electron beam if this second lens is of an axially asymmetrical type in which the downstream electrode is at a higher positive potential than the upstream electrode.

All of the individual elements of the cathode-ray tube of the present invention are well known in the art and neither their structure nor mode of operation need be described in greater detail herein.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

lclaim:

1. In a cathode-ray tube having an electron gun, a target electrode, cathode ray deflection means disposed in the path of the beam produced by said gun for deflecting the beam, said deflection means comprising first and second deflection units for deflecting the beam in two mutually perpendicular directions, a first image-forming lens, disposed in the path of the electron beam produced by the gun, for producing an intermediate image of the cross section of a selected point along the beam, a second image-forming lens disposed in the path of the beam and downstream of the first lens, with respect to the direction of travel of the beam electrons, for reproducing the intermediate image on the target electrode, the improvement wherein said first image-forming lens constitutes means for producing an intermediate image which is no greater than three times as large as the beam cross section of such selected point, wherein each of said image-forming lenses is axially symmetrical in form, in consequence of which said intermediate image is formed in all deflection direction, and wherein the power of refraction of said second image-forming lens is greater than that of said first image-forming lens.

2. The combination as defined in claim 1 wherein said cross section is that of the beam crossover point.

3. The combination as defined in claim 1 wherein the target electrode is constituted by a fluorescent screen upon which said second lens reproduces said intermediate image.

4. The combination as defined in claim 1, wherein said intermediate image is of substantially the same size as said cross section.

5. The combination as defined in claim 1, wherein at least one of said image-forming lenses is in the form of an electrostatic lens.

6. The combination as defined in claim 5 wherein said first image-forming lens is in the form of an electrostatic lens unit.

7. The combination as defined in claim 1 wherein said second image-forming lens is in the form of an electrostatic accelerator lens.

8. The combination as defined in claim 1 wherein said second image-forming lens comprises at least one additional auxiliary electrode.

9. The combination defined in claim 1 wherein said second image-forming lens is in the form of an electrostatic lens unit.

10. The combination as defined in claim I wherein each of said image-forming lenses is in the form ofa cylindrical lens.

11. A cathode ray tube as defined in claim 1 wherein said first image-forming lens is in the form ofa magnetic lens.

12. A cathode ray tube as defined in claim 1 wherein said second image-forming lens is in the form ofa magnetic lens.

13. The combination as defined in claim 1 wherein said deflection means is of the electrostatic type.

14. The combination as defined in claim 1 wherein said deflection means is of the electromagnetic type.

15. The combination as defined in claim 1 wherein said deflection means is disposed between said first lens and said second lens.

16. The combination as defined in claim 1 wherein said deflection means is disposed between said first lens and the electron gun.

17. The combination as defined in claim 1 wherein said units are disposed in two different planes and said first lens is mounted between said first and second deflection units.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,609,442 Dated September 28th, 1971 Inventor(s) Klaus Schaffernicht It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 2, change "Ulm an der Danube" to -Ulm/Danube--; after line 2, insert assignor to Telefunken Patentverwertungsgesellschaft m.b.H., Ulm/Danube, Germany. Column 1, line 27, change "post" to --postdeflection-. Column 2, line 71, change f to -f Signed and sealed this 9th day of May 1972.

ISEAL) A i; be :3 t:

EDWARD I E.FLETCI-II@JR,JR. ROBERT GO'ITSCHALK A morning Officer Commissioner of Patents ORM P0405) USCOMM-DC B0375-P69 U 5 GOVERNMENT PRINTING OFFHIE l9? 0-366-334 

1. In a cathode-ray tube having an electron gun, a target electrode, cathode ray deflection means disposed in the path of the beam produced by said gun for deflecting the beam, said deflection means comprising first and second deflection units for deflecting the beam in two mutually perpendicular directions, a first image-forming lens, disposed in the path of the electron beam produced by the gun, for producing an intermediate image of the cross section of a selected point along the beam, a second image-forming lens disposed in the path of the beam and downstream of the first lens, with respect to the direction of travel of the beam electrons, for reproducing the intermediate image on the target electrode, the improvement wherein said first image-forming lens constitutes means for producing an intermediate image which is no greater than three times as large as the beam cross section of such selected point, wherein each of said image-forming lenses is axially symmetrical in form, in consequence of which said intermediate image is formed in all deflection direction, and wherein the power of refraction of said second image-forming lens is greater than that of said first image-forming lens.
 2. The combination as defined in claim 1 wherein said cross section is that of the beam crossover point.
 3. The combination as defined in claim 1 wherein the target electrode is constituted by a fluorescent screen upon which said second lens reproduces said intermediate image.
 4. The combination as defined in claim 1, wherein said intermediate image is of substantially the same size as said cross sectioN.
 5. The combination as defined in claim 1, wherein at least one of said image-forming lenses is in the form of an electrostatic lens.
 6. The combination as defined in claim 5 wherein said first image-forming lens is in the form of an electrostatic lens unit.
 7. The combination as defined in claim 1 wherein said second image-forming lens is in the form of an electrostatic accelerator lens.
 8. The combination as defined in claim 1 wherein said second image-forming lens comprises at least one additional auxiliary electrode.
 9. The combination defined in claim 1 wherein said second image-forming lens is in the form of an electrostatic lens unit.
 10. The combination as defined in claim 1 wherein each of said image-forming lenses is in the form of a cylindrical lens.
 11. A cathode ray tube as defined in claim 1 wherein said first image-forming lens is in the form of a magnetic lens.
 12. A cathode ray tube as defined in claim 1 wherein said second image-forming lens is in the form of a magnetic lens.
 13. The combination as defined in claim 1 wherein said deflection means is of the electrostatic type.
 14. The combination as defined in claim 1 wherein said deflection means is of the electromagnetic type.
 15. The combination as defined in claim 1 wherein said deflection means is disposed between said first lens and said second lens.
 16. The combination as defined in claim 1 wherein said deflection means is disposed between said first lens and the electron gun.
 17. The combination as defined in claim 1 wherein said units are disposed in two different planes and said first lens is mounted between said first and second deflection units. 